While not limited thereto, the present invention is particularly adapted for use in analog control systems for aircraft, hydrofoils and the like where a high degree of redundancy is required for safety purposes.
In a hydrofoil seacraft, for example, the hull of the craft is lifted out of the water by means of foils which are carried on struts and usually pass through the water beneath the surface thereof. In passing through the water, and assuming that sufficient speed is attained, the foils create enough lift to raise the hull above the surface and, hence, eliminate the normal resistance encountered by a ship hull in passing through the water.
In the usual case, there are forward and aft foils both provided with control flaps similar to those used on aircraft. The other essential control element is the rudder which pierces or is submerged beneath the surface of the water and may be either forward or aft of the craft, depending upon its design. In most hydrofoils, the flaps or control surfaces are used to cause the craft to ascend or descend and to control the craft about its pitch and roll axes. However, they can also be used in combination with the rudder to bank the ship about its roll axis during a turn. Flaps are also used to stabilize the craft during movement on water so that pitching or rolling motions can be minimized by proper counterbalancing and movement of the flaps.
A control system of the type described above is disclosed and claimed in copending application Ser. No. 302,559, filed Oct. 31, 1972, now Pat. No. 3,886,884, and assigned to the assignee of the present application. In the system described in the aforesaid copending application, inboard and outboard starboard flaps are utilized on the aft foil together with inboard and outboard port flaps. These are independently controlled so as to provide a greater degree of safety in the event that one flap should fail on either port or starboard side. Additionally, separate port and starboard roll gyros are utilized. Signals from these roll gyros are applied through separate channels to the respective port and starboard flaps. In certain types of hydrofoil controls, there are three signal channels, one for the outboard starboard flap, a second for the outboard port flap, and the third of which feeds both of the inboard control flaps.
In the past, and in an attempt to improve safety, a separate direct current power source was provided for each of the signal channels leading from the roll gyros to the control flaps. Originally, it was thought that the only really dangerous hard-over condition for a hydrofoil craft was a situation wherein all four aft flaps went hard-over in a direction which produced maximum roll moment on the craft. It was for this reason that the roll function and automatic control systems for hydrofoils were divided into two separate roll channels, each provided with its own power supply. It is now recognized, however, that a hard-over condition involving only two aft flaps, if one is outboard, is potentially dangerous. This could occur in the prior art system described above where separate power supplies were provided for each signal channel. That is, if the power supply for any one channel were to fail, at least two flaps would go hard-over and produce a dangerous condition.